The present invention relates to a novel precast beam for use in constructing buildings of cementitious material where reinforcing steel rods are employed to impart strength to the resulting structure. Also, a novel method of constructing a building incorporating the precast beams of the present invention is also disclosed.
In the past, the use of precast concrete structures incorporating reinforcing steel rods has suffered from the disadvantage that the precast elements have been very expensive to manufacture and set in place in view of the close tolerances that must be observed in erecting the structure. In many instances, where the tolerances have not been observed, on site modification of the precast elements has been required which causes further delay and increased costs. In other arrangements, elaborate joining elements including welded joints have had to be employed to effect assembly of the precast elements. Not only do such devices consume valuable construction time, but also they have often materially contributed to the cost of the already expensive precast elements. In some instances, where close supervision of the construction crews has not been provided, the construction crews have been known to sever a portion of the reinforcing rods of the precast elements in order to effect installation of these elements. This obviously has the undesirable, if not dangerous, effect that the resulting structure's integrity is weakened so that subsequent separation of the precast elements can and has occurred when the walls and foundation of the building settle in the earth.
In addition to the problem of effecting structural cooperation between the reinforcing elements of the precast beams and reinforcing elements of other concrete portions of the structure that are not precast, the precast elements of the prior art have been very difficult and expensive to transport and erect, particularly where they are being employed in large structures such as office buildings, parking structures, warehouses and the like. This feature has severely limited the utility of concrete precast elements in the building trade.
The present invention overcomes the foregoing drawbacks by providing a precast element and method of use of the precast element that insures substantially increased structural integrity for the resulting structure and one which is particularly useful in connection with flooring systems that are presently in use which factor will also materially reduce building costs.
In summary, the precast element of the present invention is in the form of a spanning beam which, in one embodiment, is substantially U-shaped in cross-section having relatively short upstanding legs and a base middle portion of suitable length and width, the dimensions being dependent upon the particular design of the structure in which the precast element is to be incorporated. Reinforcing rods are embedded in the middle portion of the beam at a selected location to impart great strength to the precast beam. The middle portion together with the upstanding sidewalls which extend the length of the beam define a trough for receiving cementitious material when the floor of the structure incorporating the beam of the present invention is poured. To eliminate any camber in such beams that are reinforced with prestressing rods or tendons, relieving means in the form of slits are provided in the upstanding sidewalls of each beam at spaced intervals whereby the weight of the beam in cooperation with the relieving means will assure that the beam lies flat. Stirrups are also cast into the beam and project into the trough to assure firm bonding and to act as a mechanism to transfer shear from the later added cementitious material to the already precast cement of the beam. The reinforcing rods that are embedded into the precast trough section or midsection of the beam protrude from the ends of the beam to enable suitable connection with the after poured cement of the structure being erected.
The present invention also embraces a new method of construction which preferably utilizes the precast beam of the present invention. More specifically, as distinct from the conventional practice of setting up forms for the vertical components and pouring the cement in the vertical forms, according to the present invention, the forms for the vertical components such as the columns or walls, as the case may be, are set up and then the precast beams of the present invention or other suitable precast beams are set in place on top of the vertical forms. This has the advantage of allowing workers to easily adjust the disposition of the reinforcing elements of the precast beam together with the reinforcing elements that are inserted into the vertical forms and which are employed to give strength and rigidity to the vertical components themselves. By way of example, with the vertical forms erected, the precast beams are set over the top of the vertical forms to span the distance between two vertical forms or, if desired, to provide for a cantilevered disposition of the beam. The reinforcing rods of the precast beam and the vertical components can be intertwined before concrete is poured into the trough of the precast beam and the vertical forms. Also, additional reinforcing elements may be laid across the vertical component so as to provide continuity between the ends of adjacent precast beams which will develop the required structural continuity and also develop moment connections to resist wind and seismic load. This provides a simple and economical means of accomplishing difficult structural moment connections and avoids the necessity of employing complicated and expensive joining elements for the precast beams. Also, other precast elements or portions of the structure may be connected to the precast beam by laying across reinforcing elements between the trough area of the precast beam and the reinforcing members of such other structural elements.
When the flooring forms are set in place such as those presently in use, cementitious material is poured over the forms including into the trough of the precast beams and into the vertical form so that, after curing, a unitary structure of great strength and integrity is obtained. While the method of the present invention is particularly useful with the precast beam of the present invention, it is apparent that other types of precast beams having reinforcing elements protruding therefrom may be employed.
Other advantages of the present invention will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: